A common technique for stacking ores, other minerals and solid waste materials is to pile the material. An engineered or un-engineered pile of fragmented, un-consolidated rock, clay, gravel, solid waste or material removed or mined from the earth, of particulate material is constructed, typically over an engineered liner and liquid collection system. Older piles typically have no engineered liner or solution collection system. Natural precipitation or meteoric water is naturally applied to and percolated through the pile depending on local weather conditions, where the water contacts the material and may change the material's chemistry. The water may dissolve one or more elements, compounds or minerals that may degrade the quality of the water solution that flows from the pile, either to a collection system or to the earth adjacent to or underneath the pile. Depending on the previous reagents added to the pile and the material and mineral composition of the pile, the solution flowing from a pile may have high or low pH and may contain harmful or hazardous elements, compounds and mixtures that may impact local and regional water quality. Soil and other covers are sometimes applied on the surface of the pile to reduce or control the meteoric water with dissolved or entrained gases that flows through a pile.
Theoretically, the meteoric solution (rain or snow fall) is supposed to travel vertically through the pile in a fairly uniform manner from the starting point of each rain drop, drip point or snow melt drip. In reality, within a relatively short period of time, a path of least resistance will be formed in the pile starting at each drip point that is based on the formation or placement of the material underneath the drip point. Each path of least resistance is unlikely to be completely vertical and as a result, large sections of the pile may receive no meteoric solution initially, resulting in relatively little or no chemical changes of the piled material. Also, the chemical properties in some portions of the pile may be less conducive and reactive to the meteoric solution to the dissolution of the minerals, compounds and mixtures into the discharge solution flowing from the pile. But, after a period of time, due to capillary action and changes in the meteoric solution flow pathways, plus time dependent chemical and biochemical reactions, the chemistry of the meteoric solution can be altered. In addition, colonies of aerobic and anaerobic bacteria naturally inoculated during the placement of the pile may influence this reaction of the meteoric solution with the material in the pile. These colonies of bacteria respond differently to the chemistry of the solution that impacts their local environment. Thus, the pH, quantity of dissolved gases, chemical composition of the solution and other reagents and minerals, naturally occurring and added to the material upstream of the local environment, will dictate the local zone's chemistry and biochemistry.
Generally, a modern pile has a collection system or drainage or is located where the solution flowing from a pile is collected, quantified and may be sampled. Historic piles may not have a collection system or may have a partial one, one that leaks or is inadequate. Water quality of the solution flowing from a pile may dictate the need for treatment to clean up, remove or alter certain hazardous or toxic components found in the water so the water quality can approach the characteristics outlined by the “Clean Water Act.” Solutions are needed that will allow the physical rechanneling of solution pathways through a pile, so fluids in a pile (post stimulation) will gravitate to a downhole well, then to the bottom of a pile, thus reducing the solution retention contact with minerals and retention time in the pile.
U.S. Pat. No. 8,021,461, which is incorporated herein by reference, is directed to improving the extraction of components of interest from heaps, particularly when non-uniform leaching occurs, and involves remedial treatment of a selected portion or portions of the heap.